1. Field of the Invention
The present invention generally relates to an apparatus and method for controlling the sequential transmission of broadcast programs, for example, from a television broadcasting station.
2. Description of the Prior Art
A conventional automatic program transmission system of a television broadcasting station is illustrated in FIG. 1 to comprise a long range scheduling computer 101 which generates long-term program schedule data, for example, a data file representing a weekly schedule of programs to be transmitted by the automatic program transmission system. Real-time control over the transmission of programs by the system is exercised by a transmission control computer 102. The weekly schedule of programs to be transmitted, also referred to as a play list, is provided by the long-range scheduling computer 101 to the transmission control computer 102 either by means of a transmission line 110 or via a recording medium, such as a floppy disk 103.
The transmission control computer 102 directly controls the production of programs broadcast from the station on the basis of the play list by issuing real-time commands to a plurality of program generation devices with the aid of clock signals supplied to the computer 102 by a station reference clock. In the automatic program transmission system of FIG. 1, four such program generation devices are illustrated. These include a still image system 104 and a video tape recorder (VTR) 105. Also included is a cart machine 106, which is operative, under the control of the transmission control computer 102, to select from among a large number of video tape cassettes in a storage magazine or library one cassette on which a desired program is recorded, to load the selected cassette into a video cassette player, and to locate and reproduce the desired program recorded on the cassette tape. The system also includes a telecinematic device 107 which is adapted to transform images stored on motion picture film to video signals. Each of the program generation devices 104-107 is directly turned on and off under the control of the transmission control computer 102 which exercises such control at intervals of one thirtieth of a second.
The transmission control computer 102 is also coupled with a switching device 108 which receives the video signals produced by the program generation devices 104-107 and is operative, under the control of commands received from the transmission control computer 102, to select the signals output by one of the devices 104-107 for transmission from a broadcast antenna 109.
Since the transmission control computer 102 exercises real-time control over all of the devices 104-108, while at the same time being required to exercise supervision over the play list data, the computer 102 must be a large scale device employing relatively complex software. In the event of an interruption in the broadcast schedule (for example, when a news bulletin must be broadcast), or in the event that a previously scheduled program must be changed or replaced by another, thus requiring that the play list be modified, the computer 102 must be reprogrammed. Consequently, not only must the schedule supervisory software of the transmission control computer 102 be rewritten, which is a relatively complex task, but it is necessary to interrupt the operation of the program generation device in use at the time of reprogramming.
Since the program transmission system must rely continuously on the transmission control computer 102 for its proper operation, if operation of the computer 102 is interrupted due to a power supply problem or other malfunction, the remainder of the system, including the program generation devices 104-107 and the switching device 108, are likewise disabled.